The basic components of a modern x-ray tube consist of a high vacuum tube containing the anode/target and the cathode/electron source. The operation of the tube also requires a high voltage power supply to create an electric field between the cathode and anode, and a low voltage power supply for exciting the electron source. The general idea behind the x-ray tube has not changed significantly in the last 100 years and is relatively simple: the electron source (heated tungsten filament) is placed in the electric field that accelerates electrons towards the target (anode) and if the electrons have enough energy, they will generate x-rays when they hit the target by one of two mechanisms. The first mechanism is the Bremsstrahlung effect, where the electrons suddenly decelerate when they interact with the atoms in the anode/target. This sudden braking of the electrons causes them to lose kinetic energy and emit the difference in the form of x-rays photons and heat. The other mechanism of x-ray emission happens again when an electron reaches the anode, but instead of only being decelerated, the electron knocks out an electron from the anode material. This causes an electron from a higher energy level in the affected atom to drop down to fill this vacancy. Because the electron that will fill the vacancy comes from a higher energy level, it must emit a photon with energy equal to the difference between the energy levels involved in the process. This is referred to as a characteristic x-ray because the energy emitted is specific to the anode material, with different materials having distinct x-ray characteristic peaks.
Currently, commercial x-ray tubes utilize a heated filament as the electron source/gun. The average lifespan of a medical x-ray tube is only a few hours at normal filament heating. Refurbishing the filament is an expensive process because the pressurized tube (glass) must be opened, the filament exchanged, and then the tube must be re-sealed and evacuated to a high vacuum. Further, the x-rays cannot be rapidly pulsed due to the nature of the filament's slow heat response. Moreover, switching of the “focusing” electric field is known to strain the filament.
Therefore, there has been a long-standing need in the x-ray generation community for new methods and systems that address these and other deficiencies in the art.